Method for producing a surface acoustic wave device

Abstract

A surface acoustic wave device is so manufactured that it's reliability is increased and so that it is surface-mountable with no requirement for packaging. The surface acoustic wave device (20) has a pair of opposite interdigital electrodes (2a, 2b) and a piezoelectric member (4) in close contact with the interdigital electrodes (2a, 2b). A portion located between the pair of interdigital electrodes (2a, 2b) propagates surface acoustic waves. This device (20) is characterized by an air bridge (13) covering the portion of the piezoelectric member (4) for propagating surface acoustic waves and the pair of interdigital electrodes (2a, 2b). The air bridge (13), may be provided with an insulating film (14) which is not in contact with the piezoelectric member (4).

What is claimed is: 
     
       1. A method of manufacturing a surface acoustic wave device, comprising the following steps: (a) forming at least two pairs of interdigital electrodes (2a, 2b) and respective lead-in electrodes (3a, 3b) on a surface of a substrate,   (b) forming a first masking on said substrate outside said electrodes,   (c) forming a piezoelectric layer (4) on said electrodes,   (d) forming a second masking on said piezoelectric layer (4),   (e) forming an insulating film (5) outside said second masking where there is no piezoelectric layer (4),   (f) forming a first photo-resist film (6) on said surface of said substrate to cover all areas of said surface of said substrate,   (g) forming a groove (6a) in said photo-resist film (6) radially outwardly of said piezoelectric layer (4) to leave a photo-resist portion surrounded by said groove (6a) and a photo-resist portion outside said groove (6a),   (h) forming a gold layer (7) on said portions of said photo-resist film (6) and on a wall of said groove,   (i) forming a second photo-resist film (9) on said gold layer (7) above said surrounded photo-resist portion and at least partly above said groove (6a), said second photo-resist film (9) having lateral holes (8) therein,   (j) etching said gold layer (7) to form a gold bridge pattern (12) covering said surrounded photo-resist portion and having a plurality of bridging elements (11) outside said holes (8) in said second photo-resist film (9),   (k) removing said photo-resist films (6) and (9) through holes between neighboring bridging elements (11), whereby said gold bridge pattern (12) with its bridging elements (11) forms a gold air bridge (13) supported by said bridging elements (11) above said piezoelectric layer (4), and   (l) depositing an insulating layer (14) on said gold air bridge (13).   
     
     
       2. The method according to claim 1, wherein said piezoelectric layer is essentially composed of one or more compounds selected from the group consisting of ZnO, AlN, Pb(Zr,Ti)O 3 , (Pb,La)(Zr,Ti)O 3 , LiTaO 3 , LiNbO 3 , SiO 2 , Ta 2  O 5 , Nb 2  O 5 , BeO, Li 2  O 4  O 7 , KNbO 3 , ZnS, ZnSe and CdS. 
     
     
       3. The method according to claim 1, wherein said substrate is made of any material selected from the group consisting of diamond, diamond-like carbon, boron nitride and sapphire.